Electrical system



' Aug. "2511531;

Filed March 25, 192'? FLgJ.

III'IIIIIIL- E Inventor: Edward \XAKeIlogg.

- Patented Aug. 25, 1931 UNITED STATES PATENT OFFICE i EDWARD W.KIElLLOGG, OF SCHENEC'IADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIOCOMPANY, A CORPORATION OF NEW YORK Mormon. sYs'rEm Application filedlarch 25, 1927. Serial No. 178,476.

My invention relates to electrical systems comprising a space dischargedevice having its input circuit connected to an antenna through a localhigh frequency source, and

has for its principal object the provision of an im roved arrangementwhereby the feeding 0 energy from the input circuit into the antenna maybe prevented.

In heterodyne systems comprising an antenna and a local source oroscillator operated at a frequency slightly different from that of theantenna for producing a low frequency beat voltage, it 1s customary toconnect the oscillator, or a coil inductively com pled thereto, inseries with the antenna tuning coil, between the cathode and the grid ofthe space discharge device so that the oscillator voltage plus theantenna voltage is applied between the' grid and cathode of the device.In producing a voltage between grid and cathode of the space dischargedevice, the local source or oscillator incidentally impresses a voltageacross the antenna tuning. The oscillator voltage is in fact dividedbetween the two circuit elements, antenna tuning and grid to cathodecapacity, and the fraction of the oscillator voltage which is impressedacross the antenna tuning depends on the impedance drops through twodifferent parts of the circuit. The grid to cathode capacity reactanceis of the order of 10,000

ohms at broadcasting wavelengths. The impedance of the tuned antennacircuit varies from a few hundred ohms when the oscillator is operatedat a frequency substantially dilferentfrom that for which the antenna istuned to from 10,000 to 40,000 ohms when the oscillator frequency issubstantially the same as that for which the antenna is tuned.

As long as the frequency of the oscillator is substantially differentfrom that for which the antenna is tuned, there is little variation inthe antenna voltage produced by adjustment in the frequency oftheoscillator. In the operation of tuning in stations, however, thefrequency of the oscillator frequently crosses that for which theantenna is tuned and the antenna voltage is varied in a manner tointerfere with other receiving sets.

5 In accordance with my invention, this difnassueo ficulty is avoided byconnecting the oscillator to the input circuit in such a waythat thepotential of the grid with respect to ground I (assuming one end of theantennatuning coil' to be grounded) is substantially unaffected by theoscillator voltage, while the necessary a cathode to grid voltage isobtained by causing the cathode to vary in potential with re-,

spect to ground, at oscillator frequency.

My invention will be better'understood from the following descriptionwhen considered in connection with the accompanying drawings and itsscope will bepointed out in Y the appended claims.

, Referring to the drawings, Fig. 1 diagram:

matioally illustrates a heterodyne system wherein my invention has beenembodied; and Figs. 2 and 3 illustrate its application to slightlydifferent autodyne systems.

Fig. 1 shows a detector devicel which is provided with an input circuitcomprising a grid 2, a cathode 3, a double-wire secondary' winding 40f atransformer 5, and a tunin element 6 connected between an antenna f -er9 and a transformer winding 10, and an anode 11. A, local source ofoscillations or oscillator 12 is connected to the input circuit of thedevice 1 through a primary winding 13 and the secondary winding 4 eachturn of which is made of double wire in order to permit the transmissionof heating current to the anode 3 froma source 14 through a controlresistor 15. A winding 16, inductively related to the winding 13, isconnected to the grid 2 or high potential end of the input circuitthrough a condenser 17 for the purpose of neutralizing the effect of thecapacity couplixnlg between the grid 2 and the cathode 3.

ith these connections, the oscillator 12 causes the potential of thecathode 3 to change with respect to ground or low potential end of theinput circuit but produces little, if any, effect on the potential ofthe grid 2. Since the anode 11 is virtually grounded through "the"intermediate frequency tuning -condenser 9, there is no tendency forcurrents of oscillator'frequency to get into the antenna circuit by wayof'th'e grid to anode capacity. J The potential of the antenna 7 with i'respect to ground is thus substantially un zifiectedby the oscillatorand interference with-other receivingis avoided.

f Fig; 2 illustratesfan autodyne system wherein a' resistor 18 isconnected in the oscillator circuit topermit adjustment in in- Y tensityof'the'oscillations. V In the case of the "autodyn'e' circuit, anappreciable impedjprevious' case. Under these conditions the balancingcondenser 17 would need to be reance at oscillator frequency isintroduced by the feed back coil in the anode circuit, and 'thereforetheanode is no longer maintained at practically stationary potential as inthe adjusted in orderfthat it might balance out the electrostatic effecton the grid. of both cathode'and anode capacities. If the cou-'pling'beti'veen coil '5 and coils 4 and 16 can be maintained constant,theratio between cathode'and anode voltages at oscillation. frequencywill remain substantially constant,

and a single setting of condenser 17 will suffice for balancing outtheelectrostatic effects otboth anode and cathode on the grid potenti'al.The rheostat 18 provides means whereby the amount of feed back can becon- 'trolledwithout 'changing'the coupling between coil 13-andcoils4'and16. It should be bornein mind in following this discussionthat the output circuit 9,10, istuned for a frequency whichdiffers-widely from the os cillation frequencyand has negligibleimpedance for 1 the oscillation currents.

If it is desired to maintain the rheostat 18 at constant potential, theoscillator-tuned circuit maybe connected in series with themtermediatetuning condenser 9' as shown 1n Fig. 3.

The embodiments of the invention illustrated and described herein havebeen se-' lected for the purpose of clearly setting forth the principlesinvolved. It will be apparent,

' however, that the invention is susceptible of being modified to'meetthe dilterent conditionsencounteredinits use. For example the circuit6-7 which is represented as an antenna, mightinstead, be a receivingloop,

and it isnot necessary to have any part of the circuit actuallygrounded, the ground'indicatedin'the drawings being primarily areference potential. It is also apparent that where the cathode is ofthe radiation heated type rather than the hot filament type, the coilwould not have to be of double wire. I therefore aim to cover by theappended claims all modifications within the truespirit and scope ofmyinvention.

What I'claim as new and desire to secure by Letters Patent of theUnited'States. is 1. A radio apparatus of the heterodyne type includinga detector tube, an input circuit for said-tube having a low potentialend connected with the cathode of the tube for impressing a signalvoltage upon said tube, an output circuit'tor said tube,.means providinga common grounded connection between said output circuit and said lowpotential endof said input circuit, a source of oscillations, and meanscoupled with said source and'interposed in'circuitbetween the lowpotential end of the input circuit and said cathode for causing thecathode potential to varywith respect to'the low potential end of saidinput 'circuit.

2. A radio apparatus of the heterodync type including a detector tube,an input circuit for said tube having a low potential end connected withthe cathode of the tube for impressing a signal voltage upon said tube,

an output circuit for said tube, means providing a common groundedconnection between. said output circuit and said low potential end ofsaid inputcircuit, a source of oscillations, means coupled with saidsource and interposed in circuit between the low potential end of theinput circuit and said ing a grid, a cathode and an anode, and atuned'mput circuit connected between said grid and cathode, of means forimpressing the oscillations of said source upon said device withoutradiating the same from said tuned circuit, including a ground connection for said'input circuit, a transformer having a primary windingconnected with.- said source and a secondary winding 1nter-.

posed in circuit between the cathode and'the ground connection.

- 4. In an electrical apparatus of the high frequency heterodyne type,the combination withan'electric discharge device having a grid, an anodeand a cathode, of a ground connection, an input signal voltage circuitfor said device connected between the ground connection and the grid ofsaid device, an

output circuit connected between the ground connection and the anode,and means for applying an oscillation voltage at a difierent frequencyfrom the signal voltage interposed between the ground connection and thecathode.

5. In an electrical apparatus of the high frequency, heterodync type,the combination with an electric discharge device having a grid, ananode aniid a cathode, of a ground connection, aniiiput signal voltagecircuit for said device connected between the ground connection and thegrid of said device, an output circuit connected between the groundconnection and the anode, means for applying an oscillation voltagebetween the ground connection and the cathode, and means connectedbetween the ground connection and the grid of said device forneutralizing the connected between the ground connection and the anode,means for applying an oscillation voltage at a different frequency fromthe signal voltage between the ground connection and the cathode, andmeans for tuning said input and output circuits.

In an electrical apparatus of the high frequency, heterodyne type, thecombination with an electric discharge device having a grid, an anodeand a cathode, of a ground connection, an input signal voltage circuitfor said device connected between the ground connection and the grid ofsaid device, an output circuit connected between the ground connectionand the anode, and meansjor applying an oscillation voltage between theground connection and the cathode, and

, means for adjusting the intensitv of the oscillation voltage appliedfrom said source.

8. The combination with an electric discharge device of theself-heterodyne type having a grid. an anode, a cathode. an inputcircuit connected with the grid and an output anode circuit, of meansfor applying selfheterodyne oscillations to said device, said meansincluding a transformer having a primary connected in said outputcircuit, means connected in circuit with the primary for varying thefrequency of the self-heterodyne oscillations, means in circuit with theprimary for varying the strength of said oscillations, a secondary forsaid transformer, said secondary providing a common connection betweensaid input and output circuits and the cathode of said device, and aneutralizing means including a winding inductively coupled with saidprimary connected in parallel with the input circuit.

9. The method of heterodvning a radio signal which comprises applyingasignal voltage at a certain frequency between the grid of an electricdischarge device and ground, and simultaneously applying an oscillationvoltage at a different frequency between ground and the cathode of saiddevice.

10. The method of heterodyning a radio signal which comprises applying asignal voltage at a certain frequency between the grid of an electricdischarge device and ground, neutralizing the inter-e1ectrode capacityof the device, and simultaneously applying an oscillation voltage at adifferent frequency between ground and the cathode of said device.

In witness whereof, I have hereunto set my hand this 24th day of March1927.

EDWARD W. KELLOGG..

